Tell that to the Vietnamese, the Afghan, the Cuban, the korean, ... And arguably you might include a lot of eastern european country.
Just because the confrontation didn't happen in the country that were "enemy" didn't mean they didn't cause wars.
There is another alternative : two country not being powerful enough that they can wage a proxy war by using less powerful country. The issue is not the military power, it is the imbalance.
Tell that to the Vietnamese, the Afghan, the Cuban, the korean, ... And arguably you might include a lot of eastern european country. Just because the confrontation didn't happen in the country that were "enemy" didn't mean they didn't cause wars.